<div class="wrap">
    <img src="https://farm8.staticflickr.com/7187/6895047173_d4b1a0d798.jpg" />
    <div class="arrow"></div>
</div>

.wrap {
  position: relative;
  height:150px;
  overflow: hidden;
  width: 70%;
  margin: 0 auto;
}
.wrap img {
  width: 100%;
  height: auto;
  display: block;
}
.arrow {
  position: absolute;
  bottom: 0;
  width: 100%;
  padding-bottom:3%;
  background-color: rgba(0, 0, 0, 0.8);
}
.arrow:before, .arrow:after {
  content:'';
  position: absolute;
  bottom: 100%;
  width: 50%;
  padding-bottom:inherit;
  background-color: inherit;
}
.arrow:before {
  right: 50%;
  -ms-transform-origin: 100% 100%;
  -webkit-transform-origin: 100% 100%;
  transform-origin: 100% 100%;
  -ms-transform: skewX(45deg);
  -webkit-transform: skewX(45deg);
  transform: skewX(45deg);
}
.arrow:after {
  left: 50%;
  -ms-transform-origin: 0 100%;
  -webkit-transform-origin: 0 100%;
  transform-origin: 0 100%;
  -ms-transform: skewX(-45deg);
  -webkit-transform: skewX(-45deg);
  transform: skewX(-45deg);
}